Photodiodes are used in many different applications. For example, photodiodes may be used as part of detectors in imaging systems, such as x-ray imaging systems. In these x-ray imaging systems, x-rays produced by a source travel through an object being imaged and are detected by the detectors. In response thereto, the detectors (that include photodiodes) produce digital signals that represent the sensed energy used for subsequent processing and image reconstruction.
In known photodiode fabrication using a semiconductor wafer, an ion implant process is typically used to form the diode junction and a metal process (e.g., metallization process) is used to make electric connections. After the metal process, the wafer can no longer go through any high temperature processes used for semiconductor device fabrications. For example, the metalized portions cannot tolerate the high temperatures used for thermal oxide growth and/or ion implant activation. Accordingly, when forming a detector with an integrated diode/readout electronics device, fabrication on both sides of the semiconductor wafer involves metal processes at both sides of the wafer, such that a coordinated double-side photolithography process needs to be used. This process is not within standard complementary metal-oxide-semiconductor (CMOS) fabrication capabilities, as well as adds complexity and cost to the fabrication process.
Thus, known photodiode fabrication processes for forming devices for particular applications, such as detectors with integrated photodiode/readout electronics fabrication on both sides of the wafer for imaging systems, are directly related to the added complexity and cost of the overall process.